pDC-dependent IFN-I production in response to de novo stimulation with HSV and SIV in vitro. (A) Dot plot set showing intracellular staining of IFN-α2a. Left, SSC/IFN-α dot plot. Right, CD123/HLA-DR dot plot of gated IFN-α⁺ cells. PBMCs were stimulated 6 hours with either HSV-1 or with inactivated SIV (AT-2) or were mock stimulated. Representative data for 2 uninfected macaques are shown. (B) Spearman rank correlation analysis of IFN-I production (whole blood assay) in response to HSV and pDC concentration in blood samples for 18 uninfected macaques. (C) Longitudinal changes in IFN-I production in response to HSV. (D) Longitudinal changes in IFN-I production in response to SIV. IFN-I production per pDC is expressed as the ratio between plasma IFN-I concentration after 18 hours of stimulation and the absolute number of pDCs in whole blood samples.